This invention relates to a freeze-stable liquid blood control standard which can be used for the quality control of the measurement of blood pH and gases in the clinical laboratory.
Recently, in U.S. Pat. No. 3,973,913, one of the present inventors disclosed a stable blood control standard which comprises a sealed receptacle containing specially treated red blood cells and a gaseous head space having a volume at least equal to about the volume of said red cells. This special treatment comprises thorough washing and separating the red cells from the plasma components and mild treatment with aldehyde and retention in a buffered solution.
While the aforesaid blood control standard remains stable for extended periods of time at temperatures of about 2.degree. to 8.degree. C., it has now been found that substantially better storage stability of the gaseous and liquid phases is obtained by retaining at normally freezing temperatures below 0.degree. C. However, the subsequent thawing of the blood control standard prior to use at above freezing temperatures generally is injurious to the red cell component. Accordingly, it is a principal object of the present invention to provide a blood control standard of the foregoing type which is stable at normally freezing temperatures below 0.degree. C. both with respect to the liquid and gaseous phases and without injury to the red cells upon thawing to above said freezing temperatures.
It is known that glycerol can protect red blood cells against freeze-thaw injury as first reported by Smith, Lancet 11, 910 (1950). A more recent summary on the use of glycerol in the freezing of red blood cells is given by Meryman and Hornblower, Transfusion 12(3), 145 (1972).
It is also known that glycols such as ethylene glycol can be used for the storage of biological reference control compositions in liquid form at normally freezing temperatures as disclosed in U.S. Pat. No. 3,876,375.
However, the present blood control standard involves a unique composition that employs specially treated red cells in a buffered solution, rather than packed normal red cells, and a gaseous head space which is not contemplated by the aforesaid prior art on storage at freezing temperatures.